This is a relatively new
phylum; first observed in 1928, with the first published description in 1956.
About 100 species have been described so far, but more await description.

The
worms are tiny, usually less than 1 mm, and are found in sand which is rich in organic detritus. They live in the spaces between
the sand grains where they graze on fungi and bacteria. They move through their environment by beating
their cilia. The most striking feature of these worms is that they have jaws
and a muscular pharynx, see Gnathostomulida jenneri on the right which is found in water up to several hundred metres deep.